It is usual that the elevator installation of a building is modernized from time to time. A reason for modernization can be e.g. an increase in maintenance costs resulting from obsolescent elevator technology. It is also possible that the aim is to improve the transport capacity of the elevators by modernizing the elevator technology. New elevators are often also more space-efficient than earlier, in which case by modernizing the elevators space can be released in the building for some other use.
In particular, the modernization of an elevator installation in large buildings having many elevators can last for many months or even, in some cases, years. Prolongation of the modernization can hamper use of the building. On the other hand, the elevators should be in use also in the transition phase, when only some of the elevators are modernized and the elevator installation of the building is composed of both modernized and still unmodernized elevators. In addition, use of the elevators should be as smooth as possible from the viewpoint of an elevator passenger also in the transition phase.